A typical example of a rail vehicle wheel of the kind defined above is a so called V-wheel, where two flat rubber rings are arranged in a V (as viewed in cross section) between a central part (a wheel center with a clamp ring) and a wheel tire, the purpose of the rubber primarily being to reduce different kinds of noice emanating from a wheel moving on a rail.
There is no electrical connection between the wheel tire and the remainder of the wheel. Such a connection is required for providing the necessary earthing and for other purposes.
An external connection (by means of a copper wire) has proven unsatisfactory for different reasons: the screw for attaching the wire to the wheel tire reduces the wearing depth of the tire and the important tire strength, the external wire is highly exposed to mechanical and environmental damage, and it may even be difficult to obtain and maintain the necessary electrical connection.
An internal connection is thus more advantageous. However, several attempts to arrive at an acceptable solution have unsuccessfully been made. One such attempt was based on the teachings of DE-AS No. 23 24 060. Different reasons for the failures may be listed: too low contact pressures for obtaining the necessary connection especially when the surfaces are unclean, rusty and so forth, too high stresses on the wire or the like, difficulties at the mounting and dismounting for tire exchange, and so forth.